Prevalence and intensity of soil transmitted helminths among school children of Mendera Elementary School, Jimma, Southwest Ethiopia

Introduction Soil transmitted helminths are wide spread in developing countries and in Ethiopia the prevalence of STHs varies in different parts of the country. The aim of this study was to determine the prevalence and intensity of soil transmitted helminths among school children of Mendera Elementary School Jimma town, Southwestern Ethiopia. Methods A cross-sectional study was conducted between March 29 and April 9, 2010 to determine the prevalence and intensity of soil transmitted helminths among elementary school children. The study participants were randomly selected from class enrollment list after proportional allocation of the total sample size to each grade. Data about the background characteristics were collected using structured questionnaire. The stool samples were examined by McMaster method for the egg count which was used to determine intensity of infection. Data were analyzed using SPSS for windows version 16 and p-value less than 5% was considered as statistically significant. Results Of the total 715 stool specimens examined, 346 were positive for at least one intestinal parasite making the prevalence 48.4%. The most prevalent parasites were Ascaris lumbricoides 169 (23.6%) and Trichuris trichiura 165 (23.1%). The prevalence of soil transmitted helminth in this study was 45.6% (326/715). There was statistically significant difference in the prevalence of Trichuriasis between those who use latrine always and who use sometimes (p = 0.010). Females are two times more likely to be positive for Ascaris than males (p = 0.039). Majority of the students had light infection of soil transmitted helminths and none of them had heavy intensity of infection of Trichuriasis and hookworms. Conclusion Nearly half of the school children were infected with at least one STHs and majority of the students had light infection of soil transmitted helminths. Students who did not wash their hands after defecation were three times more likely to be positive for Ascaris infection than those who washed their hands after defecation. Therefore, measures like health information dissemination on the advantage of washing hands after defecation and on proper use of latrine should be taken into account to alleviate the problem.

Trichiura, and more than 1.3 billion with hookworms [2,3]. The greatest numbers of soil-transmitted helminths infections occur in tropical and subtropical regions of Asia, especially China, India and Southeast Asia, as well as sub-Saharan Africa. Of the 1-2 billion soiltransmitted helminths infections worldwide, approximately 300 million infections result in severe morbidity, which are associated with the heaviest worm burdens [4].
In Ethiopia parasitic helminthic infections are the second most predominant causes of outpatient morbidity [5]. Several studies indicated that the prevalence of parasitic infections were high in the lower altitudes including southwestern Ethiopia [6]. Ethiopia has one of the lowest quality drinking water supply and latrine coverage in the world. Many reports illustrated that A. Lumbricoides is the most prevalent intestinal parasite in different communities usually occurring together with Trichuris infections [7]. Hookworm infection, is also public health problem though the magnitude is lesser compared to Ascariasis [6][7][8]. Infection intensity is a key factor in understanding the morbidity of STH; although light infections are often asymptomatic, heavy infections cause an array of morbidities, including dietary deficiencies and delayed physical and cognitive development [9]. Additionally, Hookworm and T. Trichiura infections contribute to iron-deficiency anemia [9]. Moreover, estimates of the global burden due to STH range between 4.5 million and 39 million disability-adjusted life-years [9]. Several studies depicting the prevalence of intestinal parasites in general and the prevalence of soil transmitted helminths in particular were carried out in Ethiopia [10][11][12] and in different countries in the world [13][14][15][16] with varying degree of prevalence and intensity of infections. In a recent study [17] which was conducted in Jimma town to determine the prevalence of intestinal parasites 83% had at least one intestinal parasitic infection. In the same study the prevalence of T. trichiura, A. lumbricoides, and hookworms were 60.9, 40.9 and 17.5% respectively. The prevalence of T. Trichiura was highest among school age children (73.5%) followed by A. Lumbricoides (52.1%) and Hookworms (25.6%). Overall the prevalence of soil transmitted helminth in school age children was 58%. Even though, prevalence studies have been carried out in the study area no intensity study is conducted. So the purpose of the current study was to determine the prevalence and intensity of soil transmitted helminths among students of Mendera Elementary School.

Methods
This cross-sectional study was conducted between March 29 and April 9, 2010 in Mendera Elementary school located in Jimma town.
The town is located at 335Km away from Addis Ababa to the southwestern Ethiopia. The total area of the town is 102 Km 2 . The town is found in Jimma zone, one of the eleven zones in Oromia Regional State [18]. According to the 2007, population and housing census the town has a total population of 120,600, of which 60,590 are males and 60,010 are females. Temperature ranges from 12-30°C with a mean daily temperature of 19 0 C and the average annual rainfall is 800-2500mm. The town has an altitude of 1720-2010 m above sea level. The latrine coverage of the town is 91% it has water coverage of 84% [1,19].
Seven hundred fifteen students were selected from the school to participate in the study. The sample size was determined with the assumption that the proportion of STHs among the school children is 58% which is obtained from a study conducted by Amare et al. in 2007 [17]. By considering a 95% confidence level and a 5% The total sample size were allocated to different grades i.e. grade 1 to 8 of Mendera Elementary School proportional to size of each grade and the sampling frame was the students' enrollment list.
Then the study subjects were selected from the list at random using random number table.
Two trained data collectors collected all the necessary background data by using structured questionnaire. After giving adequate instruction, each study participant was provided with a stool cup, applicator stick and soft tissue paper (for cleaning) to bring 3gm of fresh stool sample of their own, which was sufficient for direct wet mount as well as for the McMaster method to count the eggs.  (Table 1).
Data were entered into a computer then cleaned and analyzed using SPSS windows version 16. Descriptive statistical methods were used to summarize the collected data. The intensity of infection was determined for A. lumbricoides, T. trichiura and Hookworms and expressed as egg per gram (epg) of feces for each student. The associations between dependent categorical variable and independent categorical variables were assessed using Chi-square.
Logistic regression was used to evaluate the effect of factors on the probability of soil transmitted helminthic infection. P-value <0.05 was taken as indicator of significant association.

Ethical clearance was obtained from Ethical Review Board of Jimma
University. Before the study was started, parents or guardians of the study subjects were gathered in different times and they were clarified about the objective of the study and finally signed on the consent form. In addition, verbal ascent was obtained from each of the study participants before they gave stool sample. All students positive for intestinal parasites were treated using appropriate drugs.

Results
Out of 822 randomly selected students 715 (87%) were volunteer to participate in the study and provide stool sample. Majority of the study participants were females (60.6%). Larger proportions (59.9%) were in the age range of 10-14 years, 48.4% were first cycle students (grade 1 to 4) and 51.6% were in grades 5 to 8 (Second cycle) ( Table 2) The prevalence of Ascaris lumbricoides was 23.6% (169/715) and there was no significant gender difference (p = 0.08) as well as between different age categories (p = 0.32). Similarly, the prevalence of Trichuris trichiura among the school children was 23.1% (165/715) and it was not significantly associated with gender and age of study participants. The prevalence of hookworms was 9.4% (67/715) ( Table 3) Summary result in Table 4  1994 [17,21,22]. Of the 715 examined students 346 were infected with one and more than one intestinal parasites. This is an indication for the rampant existence of helminthic infection among elementary school attending population of Jimma town in general and soil transmitted helminthic infection in particular. Despite the existence of high water and latrine coverage in the town, this finding seems to be higher [18,19]. This could be attributed to poor sanitary facility of the school as well as poor personal hygiene practice of the students. lumbricoides, T. trichiura and hookworm [28]. In the present study, the prevalence of single, double and triple infection by soil transmitted helminths were 35.8%, 9.1% and 0.7% respectively.
Particularly the prevalence of triple infection caused by A.
With regard to infection intensity, from the ascariasis infected students, 92%, 6% and 2% were with light, moderate and heavy infection intensities respectively. This is in disagreement with a report from Adwa in which all Ascaris infected students were with light infections. It could be explained by the fact that students of Jimma might have frequent exposure to the parasite than students of Adwa that can contribute to harboring large worm burden of A.
lumbricoides [12]. Intensity of infection is expressed as egg per gram of feces (EPG). So the arithmetic mean (±SD) egg count for A.
lumbricoides was 1994.08 (±4305.488); Which is in contrast with the finding in Wondo Genet 7343 eggs per gram of stool [10].
Similarly, the arithmetic mean (± SD) egg count for T. trichiura was 429.09 (±658.900) egg per gram of stool; which is in agreement with the finding in Wondo Genet 461 eggs per gram of stool [10]. Intestinal nematodes have been identified as a major source of chronic ill-health, compromising the growth potential and intellectual achievements of children throughout the world. The mechanisms whereby cognitive impairment may occur have been suggested to be nutritional deficiency [29]. Iron deficiency has a strong association with impaired school performance and is common in children with high-intensity hookworm infections. Another possible mechanism is that the subclinical symptoms of heavy intestinal infection reduce attention at school [29]. Hence there should be an intervention among children of school age by means of regular deworming to keep the infection intensity at low level [30].
Of all the predictors of Ascaris infection, sex and the habit of hand washing after defecation are significantly associated with ascariasis.
Because logistic regression analysis showed that females were 2 times more likely to develop Ascaris infection than males as well as those students who do not wash their hands after defecation are 3 times more likely to develop Ascaris infection than those who wash their hands after defecation. The possible explanation for sex as a predictor is that high intensity Ascaris infection is associated with other intestinal nematodes [29]. Hence in our study most of the double infected students are females. Therefore this will explain why females are 2 times more likely to develop Ascaris infection than males. Similarly, of all the predictors of hookworm infection, grade of the study subjects is significantly associated with hookworm infection. Because logistic regression analysis showed that students of higher grade are 25% less likely to develop hookworm infection than students of lower grade. This is could be due to that higher grade students are more prone to protect themselves from hookworm infection, like by avoiding drinking unprotected water, avoiding walking on bare foot.
Gender, grade level, latrine usage pattern and the habit of washing hands after defecation were found to be the associated risk factors for soil transmitted helminths whereas age range was found to be the associated risk factor for Hymenolepiasis nana infection.

Conclusion
In conclusion, nearly half of the school children examined were infected with one and/or more than one soil transmitted helminth(s). Those students who use latrine sometimes had significant Trichuriasis, than those who use always. Students who did not wash their hands after defecation were three times more  Female students were two times more likely to be infected by ascariasis than male students;  All the heavy infections identified were due to ascariasis only.

Competing interests
The authors declare that this is their original work and there is no competing interests.

Authors' contributions
Ephrem Tefera, drafted the proposal, carried out data collection and

Acknowledgments
We would like to acknowledge Jimma University for its financial support. We are also grateful for Jimma Town health office and           Other *like Birrie, spring, combination of Tap and Birrie, Tap and spring